The multi-frame rate HD image system is standardized in the SMPTE274M and SMPTE296M by the Society of Motion Picture and Television Engineers (SMPTE). The HD image system is classified into two types according to the total number of scanning lines, that is, 1125 and 750. In the former type, the number of effective lines is 1,080, the number of effective horizontal pixels is 1,920, the total number of horizontal pixels is 2200, a clock frequency is 74.25 MHz or 74.25/1.001 MHz, a scanning system is basically an interlacing scanning, and hence a field frequency is 60 Hz or 59.94 Hz.
Owing to recent development of HD broadcasting equipment, a movie is converted into electronic medium, that is, an electronic cinema system in which a film is replaced with a video tape is realized. As a result, the broadcasting equipment is required to be applicable to both a field frequency of 60 Hz interlacing scanning mode (60i mode) for a television and a frame frequency 24 Hz progressive scanning mode (24p mode) for the movie. Therefore, For an interface between appliances, it has been proposed to add modes in which a frame frequency changes by an increase of the number of ineffective horizontal pixels without changing the clock frequency and the number of horizontal effective pixels. The added frame frequency and scanning systems include a 30p mode, a 25p mode, and a 24p mode. The total number of horizontal pixels, for example in the 30p mode, is 2,200, the same as in the 60i mode, and 2,750 (2200×30/24) in the 24p mode.
In the type of the total number of lines of 750, the number of effective lines is 720, the number of effective horizontal pixels is 1,280, the total number of horizontal pixels is 1,650, a clock frequency is 74.25 MHz or 74.25/1.001 MHz, a scanning system is basically progressive scanning, and hence a frame frequency is 60 Hz or 59.94 Hz. In this type, similarly to the type of total number of lines of 1,080, a 50p mode, a 30p mode, a 25p mode, a 24p mode and others have been added. The number of horizontal pixels is 3,300 in the 30p mode, and 4,125 in the 24p mode.
A circuit diagram of a conventional multi-frame rate applicable VCR built-in type imaging apparatus is shown in FIG. 19, and an operation will be explained below by referring to FIG. 20.
A drive pulse generator 53 generates a drive pulse corresponding to a mode according to a mode switching signal issued from, for example, a microcomputer (not shown) and sends the pulse to a CCD driver 52. The CCD driver 52 converts the drive pulse into a specified voltage, and drives a CCD 51.
For example, when a 60i mode is selected, a drive pulse shown in FIG. 20B is generated. In this case of the interlace scanning, a CCD read pulse is issued in every 1/60 second, and after the reading out, two signals of upper and lower pixels are mixed in photo diodes (PDs). Herein, signals are changed in mixing pair in every field, and signals of odd and even lines are produced. Mixed signals are vertically transferred in every line in one horizontal scanning period with a vertical transfer pulse, and are sequentially issued at a rate of a drive clock (74 MHz) in every vertical transfer pulse by the horizontal transfer pulse (not shown). In a first field, an odd line signal is issued, and in a next field, similarly, an even line signal is issued. Then, as shown in FIG. 20A, a signal of one frame ( 1/30 second) is formed.
Two methods for reading out signals of, for example, the 30p mode will be explained.
In the first method, signals are read out in every 1/30 second with a drive pulse shown in FIG. 20D. Then, signals of all lines which are not mixed in PD are sequentially issued with the vertical transfer pulse and horizontal transfer pulse (not shown) in one frame period, and the signal of the 30p mode shown in FIG. 20C is obtained.
Herein, if the CCD 51 is of an interline (IT) type, the signal read out from the PD is transferred through a vertical CCD in every line in one horizontal scanning period. When the CCD captures a bright object such as a spotlight, due to a leak of the light from the photo sensor composed of the PD to the vertical transfer unit composed of the CCD, a bright stripe, i.e., so-called a smear is often generated.
A frame interline transfer (FIT) type CCD is known as a CCD capable of suppressing the smear. This CCD includes an accumulator aside from the vertical CCD and horizontal CCD. Right after all pixel signals are read out from the PD, they are transferred to the accumulator with a high speed transfer pulse in a vertical blanking time, and then, similarly to the IT type CCD, signals are sequentially issued with the vertical transfer pulse and horizontal transfer pulse. This CCD suppresses the smear by the high speed transfer, however generates a vertical black shading due to a dark current in the accumulator.
To obtain a progressive output in the total number of horizontal pixels of 1,080, for vertically-transferring all pixel signals, the vertical CCD needs to be driven with double numbers of transfer electrodes than that in an interlace scan. Therefore a transferring capacity decreases. The FIT type CCD, further, requires double stages of the high speed transfer. In order to assure a performance, a frequency or transfer time of the high speed transfer is limited. At the present, the frequency is limited to the frame rate of the 30p (60i) mode.
In the second method, to solve the problem of the transfer capacity, the CCD of multiple frame interline transfer (MFIT) type is developed and achieves a practical level for a progressive scanning. This CCD reads out and transfers a signal group of odd lines in the vertical blanking period at high speed, and then, reads out and transfers a signal group of even lines at high speed. The accumulator accumulates the signal groups of odd lines and even lines separately. In order to obtain signals of a progressive scanning, signals must be arranged properly in a frame memory or the like. In the case that signals are not arranged, after the high speed transfer with the vertical transfer pulse shown in FIG. 20F, 30p mode signals are sent out separately in odd and even fields in the interlacing system (a high speed transfer pulse after the read pulse is not shown). This is known as a segment frame (SF) system.
The interlace signal in FIG. 20A and progressive signal in FIG. 20C or FIG. 20E are issued from the CCD 51, and put into a camera signal processing circuit 54. The circuit 54 performs a specified camera process corresponding to the interlacing system or progressive system, and sends a signal for viewfinder (VF) to a VF 55, and a signal for recording to a VCR unit 56. The VF 55 displays an image corresponding to the interlacing system or progressive system, and the VCR unit 56 records and reproduces the signal depending on the mode switching signal.
In the conventional VCR built-in type imaging apparatus applicable to multi-frame rate, the VF displays the image of the progressive signal of the 30p mode, 25p mode, or 24p mode with flickering, which affects the image, because of the low frame rate. Even in the SF system, an interlacing flicker occurs which particularly makes a moving object be hardly observed because of a time difference between odd lines and even lines.
The lower the frame rate in the 25p mode, 24p mode and so on, the more the performance of the CCD deteriorates because the low frame rate increases the smear in the IT type CCD or the vertical black shading in the MFIT type CCD.
In a certain recording mode, for example, in the 24p mode, a signal is recorded at various frame rates and reproduced in the 24p mode, and thus, a variable speed reproduced signal of the 24p mode is obtained. This case requires plural interface (I/F) specifications for the camera driving mode and the VCR, and makes the circuit larger in scale. Therefore, this hardly assures both stability and reliability, and thus, is not practicable. In particular, the variable speed reproduction for the 24p mode is an essential condition for the electronic movie, and thus, is a serious issue.